Monday, August 29, 2016

Microservices and subatomic particles - an end-user perspective?

For a while now we've seen various debates around microservices, such as how they compare to SOA, whether the emphasis should be on size (micro), whether HTTP (and REST) is the preferred communication style, where and why you should adopt them as well as when you shouldn't? The list goes on and on and I've participated in a few of them.

Recently at work we've been focusing on how best to consider microservices within an existing architecture, i.e., how, why and when to breakdown so-called monoliths into microservices. We've had a number of our teams involved in these discussions, including Vert.x, WildFly Swarm and OpenShift. We've made great progress and this article isn't about that work - I'll leave it to the various teams and others to report once it's ready.

However, during this work I also went on vacation and that gave me time to ponder on life, the universe and everything microservices related! During the time away I kept coming back to two fundamental questions. The first: why use microservices? The second: how can end-users tell if they're being used to (re-) construct (distributed) applications? Much of what we've heard about microservices has been from the perspective of developers who will use microservices, not necessarily the end-user of (re-)architected applications. And of course you're probably asking a third: how does all of this relate to subatomic particles? Patience and all will be revealed.

To answer the first question, there are a lot of reasons why people, vendors, analysts etc. suggest you should consider microservices, either as a building block for new applications or, as seems more common at the moment, as a way of refactoring your existing application or service(s) which may be monolithic in nature. At the core though is the requirement to have an architecture which allows for constituent components to be developed, revised and released independently of the entire application. The so-called "Pizza Team" approach, for instance.

This then leads us nicely to the second question: how can you tell an application has been developed, or re-architected, using microservices? If you're a user of a service or application, chances are that unless the source code is available to review and you've got that inclination, "microservices enabled" isn't necessarily going to be one of the slogans used to market it. And in fact should you care? Ultimately what you're probably more interested in is a mixture of things such as cost, reliability, performance and suitability for purpose. But let's assume you do want to know. How can you tell?

Well this is where the subatomic particles come in. Given my university degree majored in physics and computing I share an equal love for both and at times when my mind wanders I like to try to see similarities between the two areas. In the past, for instance, I've used Heisenberg's Uncertainty Principle to describe weak consistency transactions protocols. This time around I was again recalling Heisenberg; those of you who have also studied physics or have a passing interest will know that the wave-particle duality of subatomic particles cannot be view directly but can be inferred, for instance using Young's Slit experiment and firing a single "particle" at two slits to observe an interference pattern which is reminiscent of those produced by wave interference. This is a pretty extreme example of how we can infer the properties of particles we cannot view directly. Others exist, including Rutherford's original experiment to infer the existence of the atomic nucleus; I'll leave that as an exercise to the interested reader, but will say it's a fascinating area of science.

Now where all of this comes full circle is that if you're an end-user of some piece of software that has been well architected and does its job, is released frequently enough for you to do your work efficiently and basically doesn't get in the way, could you tell if it was architected or re-architected using microservices? The answer in this case is most probably no. But on the flip side, suppose you've been using an application or service which is released too slowly for you (e.g., bug fixes take months to arrive), and maybe requires a rebuild of your code each time it is released. Then let's assume things change and not only do you get updates on a daily basis but they often fit seamlessly in to your own application usage. Does this mean that the developers have switched to microservices? Unfortunately the answer is no less definitive than previously because whilst a correct use of microservices would be an answer, there are other approaches which could give the same results - despite what you may have read, good software development has existed for decades.

Therefore, without looking at the code how can an end-user know whether or not microservices are being used and why is that important? It's important because there's a lot of hype around microservices at the moment and some people are making purchasing decisions based on whether or not they are present, so you probably do need some way to confirm. Architecture diagrams are great but they're no substitute for code. But if you can't see the code, it's tricky to infer one way or the other. However, on the flip side maybe as an end-user you really shouldn't care as long as you get what you want from the application/service? Good architectures and good software architects win out in the end using a variety of techniques.

Note: yeah, the other obvious analogy between microservices and subatomic particles could be that maybe microservices are the smallest divisible aspects of your application that make sense; you can't really re-factor your code smaller than a microservice in just the same way that you can't go beyond sub-atomic particles. However, since there are things smaller than subatomic I didn't want to go there.

Saturday, May 21, 2016

Fault tolerance and microservices

A while ago I wrote about microservices and the unit of failure. At the heart of that was a premise that failures happen (yes, I know, it's a surprise!) and in some ways distributed systems are defined by their ability to tolerate such failures. From the moment our industry decided to venture into the area of distributed computing there has been a need to tackle the issue of what to do when failures happen. At some point I'll complete the presentation I've been working on for a while on the topic, but suffice it to say that various approaches including transactions and replication have been utilised over the years to enable systems to continue to operate in the presence of (a finite number of) failures. One aspect of the move towards more centralised (monolithic?) systems that is often overlooked, if it is even acknowledged in the first place, is the much more simplified failure model: with correct architectural consideration, related services or components fail as a unit, removing some of the "what if?" scenarios we'd have to consider otherwise.

But what more has this got to do with microservices? Hopefully that's obvious: with any service-oriented approach to software development we are inherently moving further into a distributed system. We often hear about the added complexity that comes with microservices that is offset by the flexibility and agility they bring. When people discuss complexity they tend to focus on the obvious: the more component services that you have within your application the more difficult it can be to manage and evolve, without appropriate changes to the development culture. However, the distributed nature of microservices is fundamental and therefore so too is the fact that the failure models will be inherently more complex and must be considered from the start and not as some afterthought.

Thursday, May 19, 2016

Serverless? Really?

Our industry appears to be going through a phase of giving new or not so new approaches short names which though catchy are so inaccurate as to be meaningless and possibly dangerous. These include "containerless", when containers of one sort or another are clearly present. Now we have "serverless ".

Look, I absolutely get what's behind the term: cloud has made it so that developers don't need to worry about deploying databases, web severs or whatever is needed to run their application and also takes care of scaling and fault tolerance. But servers and databases and other infrastructure are still there because your application still needs them; just because you don't see them doesn't mean they're not there.

Wednesday, April 27, 2016

Saturday, April 23, 2016

Types of microservices

I've started to post a few things over on the new Red Hat Developer Blog. My first entry was about microservices.

Thursday, April 21, 2016

You keep using that word (REST) and I don't think it means what you think it does

A long time ago in a galaxy far, far away ... OK, not quite. But some time ago our industry spent a lot of time and effort on discussion the pros and cons of REST, SOA, SOAP (!) etc. I even had a few things to say on the subject myself. To misquote Jeff Wayne, "minds immeasurably superior to my own" on the topic of REST and HTTP at the time had a lot more to say and do in this area. It's something which is easily Googled these days. Covered in books too. Probably even several video master classes on the topic of REST and HTTP, let alone their relevance to SOA. And yet it seems that some people either have a very short memory, didn't understand what was said, or perhaps didn't do their homework?

I'm specifically talking about how REST plays into the recent microservices wave. Yes, I think there are some problem areas with microservices and yes, one of them is the dogmatic assertion by some that REST (they tend to really mean HTTP) is mandatory. I don't believe that. I do believe that different message exchange patterns may be suitable for a range of microservices and to limit ourselves to just one (HTTP) does not make sense.

Oh and yes, it still frustrates me to this day when people talk about REST and they're really talking about HTTP - my only consolation here is that if I find it frustrating it must really annoy the h*ll out of the RESTafarians! Not all REST is HTTP and likewise not everything which uses HTTP is necessarily REST. Simple, huh? Well you'd think ...

Anyway, putting that aside, what's got me more frustrated recently is that some people are suggesting that REST (really HTTP) can't do async for microservices and therefore can prevent you breaking apart your monolith. I'm not even going to attempt to explain in detail here how that is wrong except to suggest that a) those people should go and read some InfoQ articles from the early 2000's (yes, even theserverside had things to say on the topic), b) do a Google search, c) read something from my friend/colleague Jim WebberSavas and others on the topic of REST (and maybe Restbucks - hint, hint), d) in case they're confused between REST and HTTP, maybe go and read the HTTP response codes and look at those in the early 200's range (again, another hint). As I said above, I'm not suggesting there aren't some issues with REST/HTTP for microservices. And as I've also said over the last decade or so, maybe there are some issues with building some types of distributed systems with REST/HTTP. But this isn't one of them!

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And this then brings me to a related topic. And if he hadn't been saying it around REST, I'm pretty sure Inigo Montoya would've been saying "You keep using that word. I do not think it means what you think it means" about "asynchronous". Yes, some of the authors try to make the distinction between a blocking call within a single address space and a one way interaction with a service across the network, but that really doesn't instil me with confidence that they know what they're talking about. If they threw in a bit of Fischer, Lynch and Patterson, rather than the oft overused reference to CAP, then maybe I'd be slightly less concerned. But that'd require some homework again, which they don't appear to want to do! Oh well, good luck to those who follow them!

Note, I have deliberately not included many links to things in the post in the hopes it will encourage the reader to follow up.

Wednesday, April 06, 2016

Micromonoliths?

I'm not even sure it's a word, but I wrote something on micromonoliths elsewhere - basically just some words on architecture.

Some cross postings on microservices

As I mentioned earlier, I've had some time on holiday recently and spent some time musing on microservices amongst other things. I've written a couple of articles over on my JBoss.org blog, one on microservices and co-location, and one about the mad rush to make everything a microservice. As Rod Serling often said: submitted for your approval.